Trane TRG-TRC011-EN manual Capacity Control

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period three

Capacity Control

notes

its way into the chiller through any available path. As explained earlier, the pressure and temperature inside the evaporator are determined by the concentration and temperature of the solution in the absorber. If air leaks into the chiller, however, the evaporator pressure increases because a portion of the volume inside the evaporator–absorber sections is taken up by air, which is not absorbed by the lithium bromide solution. This increase in the evaporator pressure results in higher evaporator temperatures and decreased capacities.

Sensing the increasing temperature of the chilled water leaving the evaporator, the chiller control system attempts to overcome the condition by increasing the amount of solution delivered to the generator and by increasing the amount of heat input to the generator. This causes more refrigerant to be boiled off in the generator and results in a more concentrated solution being delivered to the heat exchanger. Under higher load conditions, it is possible to increase this solution concentration to the point where crystallization occurs in the heat exchanger.

In most modern absorption chillers, high-quality construction, smart microelectronic controls, and automatic purge systems are extremely effective in removing air from inside the chiller, maintaining chiller capacity, and avoiding crystallization. Any leaks, however, should be addressed immediately.

▲

◆Decreases temperature of dilute solution traveling to generator

◆Results in lower temperature of concentrated solution returning to absorber

◆Causes concentrated solution inside heat exchanger to crystallize

Figure 48

Cooling water that is too cold, combined with a high load on the chiller, is another possible cause of crystallization. Colder cooling water causes the temperature of the dilute solution travelling from the absorber to the generator to drop. This cool dilute solution entering the heat exchanger absorbs a greater amount of heat from the concentrated solution and, therefore, results in a lower temperature of concentrated solution leaving the heat exchanger. If the temperature drops low enough, crystallization of the concentrated solution can occur.

In the past, absorption chillers were designed to operate with constant- temperature cooling water. With these chillers, a sudden drop in the temperature of the cooling water could result in crystallization. The microelectronic controls for many modern absorption chillers are designed to

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TRG-TRC011-EN

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Contents Air Conditioning Clinic Absorption Water Chillers Absorption Water Chillers Preface Contents TRG-TRC004-EN Introduction TRG-TRC011-EN Period one Absorption Refrigeration CyclePeriod one Reject heat Heat energy Absorption System Fluids High affinity for water refrigerant Components of the Absorption Cycle Conditions Steam or Hot waterrefrigerant vapor Generator Condenser Refrigerant then flows into the evaporator pan Absorber spray pump Solution Heat Exchanger Dilute Generator pump Equilibrium Chart Heat Solution temperature Period two Absorption Chiller TypesSingle-Effect Chiller Absorber Evaporator spray pump Spray pump Generator pump Double-Effect Chiller Vapor Low Temperature condenser Cooling Generator Water Evaporator Absorber Low-temperature generator pump Generator pump Absorption Chiller Types Direct-Fired Chiller Evaporator High-temperature high-temperature Generatorgenerator pump Chiller/Heater Absorption Chiller Types Changeover Absorption Chiller Types Period three Capacity ControlPeriod three Energy valve Generator Crystallization 10C 37.8C Capacity Control Capacity Control Capacity Control Heat exchanger bypass Evaporator pan Purge System Isolation valve Period four Maintenance ConsiderationsPeriod four Maintenance Considerations Test run with alternate fuel, if dual-fuel burner Maintenance Considerations Maintenance Considerations Corrosion inhibitor and performance additive recommendations Period five Application ConsiderationsCooling-Water Temperature Limitations Combination Chiller Plants 58F Special Considerations for Direct-Fired Chillers Application Considerations Equipment Rating Standards Period six ReviewPeriod six Review Review Review Questions for Period QuizQuiz TRG-TRC011-EN Answers Glossary Glossary Glossary Trane Company
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